CVE-2025-4120: Netgear JWNR2000v2 Buffer Overflow Flaw

CVE-2025-4120 Overview

CVE-2025-4120 is a buffer overflow vulnerability affecting the Netgear JWNR2000v2 wireless router running firmware version 1.0.0.11. The flaw resides in the function sub_4238E8, where improper handling of the host argument enables memory corruption. An attacker with low-privileged network access can trigger the overflow remotely without user interaction. Successful exploitation can result in memory corruption affecting confidentiality, integrity, and availability of the device. The vulnerability is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-120] (Classic Buffer Overflow). The vendor was contacted prior to disclosure but did not respond.

Critical Impact
Remote attackers with low privileges can trigger a buffer overflow in the JWNR2000v2 router firmware, potentially leading to arbitrary code execution or device compromise.

Affected Products

Netgear JWNR2000v2 (hardware)
Netgear JWNR2000v2 Firmware version 1.0.0.11
Devices exposing the vulnerable sub_4238E8 function via the network interface

Discovery Timeline

2025-04-30 - CVE-2025-4120 published to the National Vulnerability Database (NVD)
2025-05-13 - Last updated in NVD database

Technical Details for CVE-2025-4120

Vulnerability Analysis

The vulnerability exists in the function sub_4238E8 within the JWNR2000v2 firmware image. The function processes the host argument without sufficient bounds checking, allowing input of attacker-controlled length to exceed the allocated buffer. Once the buffer boundary is breached, adjacent memory structures, including return addresses and saved registers on the stack, can be overwritten.

Because the router runs on a constrained embedded Linux environment without modern exploit mitigations such as address space layout randomization (ASLR) or stack canaries, an attacker who controls the overflow contents can redirect execution flow. The result is potential remote code execution on the device with the privileges of the affected service process.

The vulnerability is reachable over the network. An attacker who has low-privileged authenticated access to the router management surface can deliver the malicious host value remotely.

Root Cause

The root cause is the absence of length validation on the host argument before it is copied into a fixed-size buffer inside sub_4238E8. This is a classic stack or heap buffer overflow pattern common in embedded router firmware that relies on unsafe C string functions such as strcpy or sprintf.

Attack Vector

An attacker reaches the vulnerable code path over the network by sending a crafted request containing an oversized host parameter. Authentication requirements are limited to low-privileged credentials, which on consumer-grade routers are often default or trivially obtained. Successful exploitation requires no user interaction on the victim side.

No verified public exploit code is currently available. The technical write-up is referenced in the GitHub PoC Repository and the VulDB entry.

Detection Methods for CVE-2025-4120

Indicators of Compromise

Unusually long host field values in router HTTP request logs or syslog output
Unexpected reboots, crashes, or service restarts on JWNR2000v2 devices
Outbound connections from the router to unknown infrastructure following malformed inbound requests
Modified firmware checksums or unexplained configuration changes on the device

Detection Strategies

Inspect network traffic to the router management interface for oversized parameter values, particularly the host argument
Correlate router crash events with preceding HTTP requests to identify exploitation attempts
Monitor for repeated requests from the same source attempting to access internal router functions
Apply intrusion detection signatures that flag malformed HTTP headers targeting embedded device management endpoints

Monitoring Recommendations

Forward router syslog and debug output to a centralized logging platform for retention and analysis
Track all administrative authentication events against the router, including failed and successful low-privilege logins
Alert on management interface exposure to untrusted networks or the public internet
Baseline normal request patterns to the router web interface and flag statistical anomalies

How to Mitigate CVE-2025-4120

Immediate Actions Required

Restrict access to the router management interface to trusted internal hosts only and block WAN-side management
Change default and weak administrative credentials to strong, unique passwords
Segment the affected JWNR2000v2 device onto an isolated network segment until remediation is available
Plan replacement of the JWNR2000v2 with a currently supported router model given the absence of vendor response

Patch Information

No vendor patch is available at the time of publication. According to the disclosure record, Netgear was contacted but did not respond. The JWNR2000v2 is a legacy consumer router, and organizations should treat the device as end-of-life and prioritize replacement. Refer to the Netgear Official Website for any future advisories.

Workarounds

Disable remote management features on the router to reduce the network-reachable attack surface
Place the device behind a separate firewall that filters inbound requests to its management ports
Restrict LAN-side access to the management interface using access control lists or VLAN segmentation
Replace the device with a vendor-supported router that receives regular firmware updates

bash

# Example: block external access to router management ports at an upstream firewall
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 23 -j DROP